The present invention relates in general to milling tools, and in particular, to a new and useful cutting plate for milling tools.
European patent document EP-A-0392730 discloses an indexable insert in a conventional milling tool, with straight cutting edge. The indexable insert is set at an angle to the axis of the shaft of the tool. The result is a tool in which the rake angle and the clearance angle change continuously. Since this is disadvantageous, it is here suggested to implement the true rake and the back in such a way that they are curved in order to achieve the effect wherein the clearance angle and the rake angle are essentially invariably constant over the length of the cutting edge. This reference does not disclose the shapes of the chip guide and back. The application of the suggested cutting edge shape on cutter plates with a true rake could lead to elliptical curves when viewed from the top for the edges limiting the true rake. But the divergence of these curves would subsequently extend toward the front face because the cutter plate is installed with such slope to the shaft axis that the front-face region of the cutting edge precedes the end of the cutting edge facing the driving side. This leads to the disadvantage that the shaft thickness under the bottom of the cutting plate is thinned.
German patent document DE-A-36 18 574 discloses an indexable insert whose top surface is doubly curved, namely it comprises a combined convex-concave curvature. The rake angle is said to be constant and positive along the cutting edge. The axial true rake angle, thus the angle at which the cutting edge is inclined toward the rotation axis of the shaft, is selected such that the front-face end of the cutting edge leads. The double curvature of the true rake leads to the fact that the exit edge falls within the region of the second main cutting edge, which means that these two edges, in top view onto the cutter plate, do not diverge from the front face. In the case of cutter plates for small shaft diameters the stability of the tool is problematic because the shaft in the region of the plate support is strongly thinned.